dos.yaml Reference

The dos.yaml file provides the controls to blacklist IP addresses or
subnets to protect your app from Denial of Service (DOS) attacks or similar
forms of abuse. For more information, see
Configuring DoS protection.

By default, App Engine serves a generic error page to blacklisted addresses. You
can configure your app to serve a custom response instead. For details, see the
app.yaml reference on error handlers.